Process of heat treating nylon filaments by passing them around a heated metal drum



June 4, 195

J. CHENEY, JR 2,794,700

A. PROCESS OF HEAT TREATING NYLON FILAMENTS BY PAS'SIN THEM AROUND A HEATED METALDRUM Filgad July 1, 1954 Fi f 2 v CHAROMIUMA PLATED HEATED SURFACE INVENTOR gAZRO J. CHENEY JR.

ATTORNEY I Patented June 4, 1957 PRGCESS OF MAT TREATING NYLON FILA- MENT BY PASSING THEM AROUND A HEATED PAETAL DRUM Azro Jackson Cheney, In, Wilmington, Del., a ssignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Application July 1, 1954, Serial No. 440,707

1 Claim. (Cl. 8-1301) This invention relates to the conditioning of filaments of synthetic linear polyamides to improve recovery from bending of hot-drawn filaments to be used as bristles, fish-line leaders, musical instrument strings, etc.

It has been known heretofore that oriented filaments of fiber-forming synthetic linear polyamides can be improved by maintaining the same in liquid water at temperatures of at least 85 C., or in steam or hot air, while held in a predetermined shape for a controlled period of time until a substantial improvement in recovery from deformation takes place (U. S. 2,226,529, issued December 31, 1940, to Paul R. Austin; cf. also British Patent 598,820, accepted February 26, 1948).

The conditioning procedure for drawn filaments, hereinabove mentioned, has given satisfactory results for many years, but it is a process which requires excessive maintenance and investment costs, as well as high operating costs. Thread-up in the process is awkward, and for this reason integration with spooling machines and tapered filament cutters gives rise to diificulfies which it would be profitable to avoid. A preferred form of this prior art process involves an exposure time of thirty to ninety seconds in a hot-air chamber, heated electrically, this holdup in the chamber being attained by taking about forty passes around two skewed rolls each having a diameter of about four feet. it is evident that such equipment as this entails substantial investment cost, and, with auxiliary equipment, requires a floor area which is somewhat larger than would be needed for simpler types of equipment, should such simplification be found to be practicable. Moreover, in practice, it has been found necessary, in operating the above-identified prior art conditioning method, to use scrap filament during and after thread-up, and until the temperature has reached the desired level, since threading-up at operating temperature is not practically feasible. When the proper conditioning temperature is reached the filament from the drawing equipment is tied to this scrap filament, and as the good filament leaves the conditioner, it is transferred to a new wind-up position and the filament sent through the conditioner up to this point is scrapped. For obvious reasons this part of the process leaves much to be desired, to eliminate awkwardness and eliminate waste, not only of product but also of electric power, especially during the heat-up period, and through the escape of heated air from the conditioning zone.

An object of this invention is to provide improvements in the hereinabove described process for conditioning drawn filaments.

It has been discovered in accordance with this invention that filaments composed of synthetic linear polycarbonamides can be conditioned at contact times which vary with the diameter of the monofilament or rope made up of strands thereof, by passage over a heated drum or roll at a temperature of 165 to 205 C. This contact time varies from about 0.5 second for 6-n1il monofilament to about 11.5 seconds for 40-mil monofilament, and about 1.7 seconds for a flattened 160-strand rope of 4-mil monofilament. The monofilament in all instances, when the contact time was as just specified, had bending recovery properties essentially the same as those of the conditioned drawn filaments of the same diameter, made by the prior art process hereinabove described. This was true for the monofilaments present in the rope, as well as those conditioned individually. The monofilament may be in the form of single strands or may be in the form of rope having as many as 250 strands. In general, the contact time should be about 0.08 to 0.3 second for each mil of thickness. The thickness of the individual monofilaments should be from 2 to 60 mils.

It is to be understood that the present invention differs from various previously known devices for subjecting oriented filaments or films to the action of rotating rolls. For example, in U. S. Patent 2,199,411, issued to E. V. Lewis on May 7, 1940, passage of oriented filaments over numerous rolls with a variety of functions is disclosed, yet a grooved hot plate rather than heated rollers is employed for heat-setting the said filaments. In the said Lewis patent various methods for continuous heat shrinkage of filaments, to reduce residual shrinkage thereof after orientation, are disclosed, including passing polyamide yarn continuously in contact with a dry heated surface (e. g. a heated block) at low tension, preferably at to C. The contact time of the yarn with the block was, in a typical example, in the U. S. 2,199,441, 0.12 second for 45 denier, 15-filament yarn. This type of apparatus results in undue scufiing when used with monofilament, especially monofilament of relatively large diameter, and more especially monofilament with variable cross section such as that which is subsequently to be cut into tapered bristle. Also, for any monofilament except that of very small diameter the length of the apparatus required in this prior art device is unduly long.

In the practice of this invention it is preferable to use a heated roll of relatively large diameter, e. g. about three feet, although a smaller diameter roll, having a diameter of 15 inches has also been used successfully for the same purpose. The width of the roll or drum may be varied as desired, a suitable width being about one foot. Of course, the number of passes around the roll is determined by the size of the roll and the desired contact time.

A skewed roll of much smaller diameter (e. g. 3 inches) may -be used to provide self-advancement of the filament across the width of the heated roll, particularly when more than one pass is used around the main roll.

Heating of the roll can be accomplished by any convenient means, such as electric heaters, steam, etc. Any suitable means of supporting the shaft may be used, but is generally preferred to use ballor roller-bearings which are lubricated with circulated oil, since the entire device usually operates at temperatures above those most commonly encountered in lubricated rolleror ball-bearing assemblies.

The invention is illustrated further by means of the accompanying drawing.

Figure 1 is an end view of a rotating heated drum 1 (diameter, 3 feet) around the periphery of which synthetic linear polycarbonamide filament is wound, the speed of rotation and the number of loops of filament being so controlled as to produce the desired contact time between the filament (which is fed continuously to the drum) and the peripheral surface. The loops pass over a skewed roll 2 to assure self-advancement of the filament. The peripheral surface may be chromiumplated as shown in Figure 2 to prevent rusting, but any metal or other efiicient heat conductor can be used as the material of construction for the peripheral portions of the drum. The filament which is fed is oriented filament, and the conditioning process which occurs upon contact of the filament with the drum does not result in free shrinkage of the oriented filament. Figure 2 is a side view of the same drum 1, mounted on the support 3, which also supports a variable speed drive 4 to control feed tension.

Example 1.In an apparatus of the kind described in the drawing, nylon (synthetic linear polycarbonamide) filament was conditioned, as reported in the following table. means the ability of an individual filament, in an empirical, but comparative, test to return to a straight form upon cooling to room temperature after conditioning in boiling water while wrapped around a mandrel substantially larger than the diameter of the filament. The percentage figure represents the approximate extent to which the test specimen returns to the straight form (100% being full return to straight line, and being no change in the coiled monofilament). For practical commercial operations a recovery of at least 45% is preferred for many applications.

TABLE I Conditioning of nylon filament 15-inch diameter heated metal roll {Single strand filament] Filament Properties Contact Tension on R011 Tem era- 'Iime, Filament, ure, Seconds Grams Recovery, Stitmess Percent G-Mil hexamethylene polyadlpamide at 750 feet per minute,

(not conditioned) 5 377, 000 0. 5 25 370 62 320, 000 1. 0 25 385 58 380, 000

-Mi1 hexamethylene polysebacamide at 400 feet per minute 17-Mil hexamethylene polysebacamide at 400 feet per minute (not conditioned) 0 257, 000 3. 5 100 340 49 390, 000 3. 5 200 340 51 390, 000 3. 5 600 340 55 450, 000

40-Mil hexamethylene polysebacamide at 120 feet per minute (not conditioned) 8 53-Mil hexamethylene polysebacamide at 100 feet per minute (not conditioned) 14 The term Recovery, percent as used herein Example 2.ln the above-described apparatus a strand rope of 4-mil filament was conditioned as reported in the following table.

TABLE II Conditioning 0 nylon filament 15-inch diameter heated metal roll [mo-strand rope of 4-mil filament] Contact Roll RecoveryPercent Time, Tension, Temper- Seconds Grams ature,

F. High Low Aver.

Hot Air Conditioned 80 67 73 1.7 600 330 72 38 r 57 3. 5 600 330 59 48 54 The synthetic linear polyamides which are employed in the practice of this invention are those which are discussed in U. S. Patents 2,071,250, 2,071,252, 2,071,253, and 2,130,948.

Typical examples of these polyamides, which have recurring intralinear carbonamide groups as an integral part of the main polymer chain, are hexamethylene polyadipamide, hexamethylene polysebacamide and polycaprolactum.

I claim:

A method for heat conditioning of oriented monofilament having a diameter of 2 to 60 mils, and composed of a synthetic linear polycarbonamide having intralinear carbonamide groups as an integral part of the main polymer chain while preventing scuffing of the same, which consists in contacting said filament with the periphery of a rotating metal drum, having a diameter of from 15 inches to 3 feet, heated to a temperature of to 205 C., the speed of rotation of said drum and the number of Wraps of the said filament around the said drum being such that the time of contact of the filament with the drum periphery is within the range of 0.08 to 0.3 second per each mil of thickness of the said polyamide in contact withthe peripheral surface, and continuously withdrawing said filament from said periphery surface as said filament is being fed thereto, whereby the recovery properties of the said filament, on deformation, are improved to substantially the same extent as by heating in air at the same temperature for a longer period of time.

References Cited in the file of this patent UNITED STATES PATENTS 2,199,411 Lewis May 7, 1940 2,278,888 Lewis Apr. 7, 1942 2,291,873 Brubaker Aug. 4, 1942 2,365,931 Benger Dec. 26, 1944 2,488,937 Roberts Nov. 22, 1949 

